The present invention relates to balance mechanisms for rotating machinery, particularly balance shafts for multi-cylinder internal combustion engines which exhibit shaking forces and/or rotating imbalanced couples.
Balance shafts are commonly used to reduce or cancel shaking forces and/or vibrations which result from residual imbalances inherent in the design architecture of machinery with rotating parts or mechanisms, such as motors. These balance shafts are often called xe2x80x9ccounterbalancexe2x80x9d shafts.
Balance shafts are particularly valuable when operator or passenger comfort and freedom from noise and vibration-related fatigue or distraction are desired, as in the case of motor vehicles such as automobiles, motorcycles, and the like. It is also advantageous to minimize vibration from the standpoint of equipment reliability. Where vibrations are reduced, the size, mass and/or complexity of the mounting structures can often also be reliably reduced, thus potentially reducing cost.
Some multi-cylinder motor vehicle engines, such as the 90-degree V-6 engines (i.e., 6-cylinder engines with two sets of three cylinders positioned 90-degrees apart), produce resultant imbalanced forces in the form of a crankshaft-speed rotating couple. These engines benefit from a single balance shaft with two balance weights, or masses, on opposite sides of its axis of rotation, but spaced apart axially, so as to have a dynamic imbalance providing a rotating couple. The couple produced by the balance shaft is designed to oppose or cancel that of the engine when the shaft is rotating at crankshaft speed and in the opposite directions of the crankshaft. The axial location of this xe2x80x9crotating couplexe2x80x9d-type shaft relative to the engine is not critical as the output of the balance shaft is a pure couple or torque on the crankcase.
Inline four-cylinder engines also benefit from balance shafts, although for different reasons than V-6 engines and due to different vibrating characteristics. Balance shafts for inline four-cylinder engines typically are paired to rotate in opposite directions at twice the engine speed. The two balance shafts cancel each other""s lateral shaking forces while opposing the vertical secondary shaking forces that are typical with this type of engine. Each shaft produces a single unbalance force, which taken together with its mating shaft""s unbalance force, produces a resultant vertical shaking force located centrally among the bank of cylinders. These xe2x80x9csingle unbalancexe2x80x9d type shafts are shown, for example, in U.S. Pat. No. 4,819,505.
Balance shafts can be rotated in the same direction as the engine crankshaft, or in the opposite direction, as required for the particular engine. Some engines require a pair of balance shafts rotating in opposite directions. Balance shafts typically have an elongated support member and one or more weights (often called xe2x80x9cbobweightsxe2x80x9d). The bobweights can be positioned on the same side or on opposite sides of the support member, as required.
One conventional type of balance shaft for a 90xc2x0 V-6 engine comprises a pair of opposed bobweights positioned between a pair of bearing surfaces at the two outer ends of the shaft. The bearing surfaces are supported in bearings which allow the balance shaft to rotate in accordance with the speed of the engine. A drive member at one end is connected to a gear which is driven by the engine which, in turn, rotates the balance shaft. This balance shaft is normally driven at the speed of the crankshaft of the engine and thus at twice the speed of the camshaft.
One type of improved balance shaft is shown in U.S. Pat. No. 5,483,932 which issued on Jan. 16, 1996, is entitled xe2x80x9cHollow Balance Shaftxe2x80x9d, and is commonly owned with the present invention. The balance shaft in the ""932 patent is stiffer than known balance shafts and can rotate at increased speeds without harmful bending or adversely affecting the bearings. In accordance with the ""932 patent, the balance shaft has a hollow tube with plugs positioned in each end. The disclosure of U.S. Pat. No. 5,483,932 is hereby incorporated by reference herein.
Another improved balance shaft is disclosed in U.S. Pat. No. 5,857,388, which was filed on Jul. 9, 1996 and is entitled xe2x80x9cBalance Shafts Having Minimal Massxe2x80x9d. The disclosure of that patent application is also hereby incorporated by reference herein. In accordance with U.S. Pat. No. 5,857,388 the bobweights on the balance shafts have curved surfaces which are representations of hyperbolic curves or reasonable approximations thereof, and the connector portions preferably are shaped like I-beams with concave sides, both features designed to reduce the weight and cost of the balance shafts.
It is an object of the present invention to provide improved balance shafts for automobile engines which can balance or neutralize engine noise and vibration forces. It is another object of the present invention to provide balance shafts which are stiffer and lighter than traditional balance shafts.
It is still another object of the present invention to provide balance shafts which can rotate at a predetermined speed without bending or causing excessive bearing wear. It is a further object of the present invention to provide means for securing bobweights in hollow tubular structures in order to provide improved, light-weight balance shafts.
Other benefits, features and advantages of the present invention will become apparent from the following description, when taken in accordance with the appended claims and accompanying drawings.
The present invention provides an improved balance shaft which is stiffer than known balance shafts, has the ability to rotate at increased speed without harmful bending or adversely affecting the bearings, and is lighter in weight and potentially has lower manufacturing costs than known balance shafts. The balance shaft has a hollow tubular structure which preferably is made of a deep drawn material and enclosed at one or both ends. One or more balance weights are positioned inside the hollow structure and held in place by various means, such as welding, brazing, mechanically fastening, and the like. Alternative mechanisms for securing and aligning the weights in the hollow structure include, for example, foam material, ring members, support members, indexing structures, and/or biasing members (springs, etc.).
Preferably, for 90xc2x0 V-6 engines, the balance weights that are positioned in the hollow tubular structure have a generally hyperbolic shaped surface. The hyperbolic curve represents a locus of constant contribution to the unbalanced couple produced by the shaft. This also results in lighter weight and thus also potentially lowers cost by means of improved utilization of materials in the balance weight areas of the balance shaft.
Preferably, for four-cylinder engines, a single balance weight is provided in a hollow tubular structure. The balance weight is fixedly secured in the structure, has a uniform cross-section throughout its length, and is centrally positioned in the tubular structure.
For rotation, bearing mechanisms, such as ball bearing members, are positioned at two or more points on the outer surface of the hollow tubular structures. Also, one of the ends of the balance shafts is formed or provided with a drive member or extended portion which is adapted to be rotated by a belt, chain or gear drive. For this purpose, a driving gear is positioned on the drive member.
The present invention has many significant advantages over known balance shafts. The inventive balance shafts are lighter and potentially less expensive than known balance shafts and do not sacrifice strength or durability. With less weight and less deflection, smaller and less expensive components, such as smaller bearing members, can be utilized. Also, the lighter weight can create less friction in the system possibly utilizing less horsepower of the engine to turn the balance shafts, thereby creating additional savings in weight and cost in the engine and vehicle. The smoother and more uniform external surface of the tubular balance shafts also allows the balance shafts to rotate more easily through the oil or fluid in the engine creating less frothing and less drag.
The one-piece tubular member utilized in the inventive balance shafts provides a stronger and more homogeneous structure with fewer joints and less components. In this regard, a one-piece tubular xe2x80x9cbottlexe2x80x9d structure with one xe2x80x9cclosedxe2x80x9d end and one xe2x80x9copenxe2x80x9d end has the fewest components and fewest joints in accordance with the present invention.
By eliminating the heavy connection members between bobweights (on conventional V-6 or similar engines) or between a bearing member and a bobweight (on conventional inline 4-cylinder engines), the present invention provides a lighter product which is smaller, has less bending or deflection, and is potentially less expensive. In this regard, smaller bobweights and thinner materials can be utilized. Positioning the bobweights under the bearing journals also saves weight, increases rigidity or stiffness (less subject to bending), and reduces the size and length of the balance shaft necessary for its purpose.
These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and appended claims.